Automatic control of the flow of bulk materials on conveyors



June 30, 1964 T. L. MELL 3,139,217

' AUTOMATIC CONTROL. OF THE FLOW OF BULK MATERIALS 0N CONVEYORS FiledJuly 31, 1961 3 Sheets-Sheet l Oomroller June 30, 1964 T. L. MELL 3, 7

AUTOMATIC CONTROL OF THE FLOW OF BULK MATERIALS ON CONVEYORS Filed July31, 1961 3 Sheets$heec 2 PrImarY Variable Slgnul Controller ,26

ConrroHer THOMAS L.MELL

ATTYS.

NVENTOR.

June 30, 1964 T. L. MELL 3,139,217

AUTOMATIC CONTROL OF THE mow OF BULK MATERIALS ON CONVEYORS Filed July31, 1961 s Sheets-Sheet 5 INVENTOR. THOMAS 1.. MELL BY W ATTYS' UnitedStates Patent 3,139,217 AUTOMATIC CQNTROL OF THE FLOW 0F BULK MATERIALS0N CONVEYORS Thomas L. Mell, Paoii, Pat, .assignor to Trans-WeighCompany, King of Prussia, Pa., a corporation of Pennsylvania Filed July31, 1961, Ser. No.'128,079 5 Claims. (Cl. 222-57) This invention relatesto the automatic control of the flow of bulk materials onconveyors andhas for an object the provision of a means for controlling the weight ofmaterial on the conveyor uniformly in accordance with a predeterminedweight in manner such that the rate of correction in the feed ofmaterial .to the conveyor is in proportion to the conveyor speed.

Systems of the type to which the present invention is applicablegenerally employ a conveyor to which bulk material is delivered by afeeder and the material travels a considerable distance before itreaches the discharge end of the conveyor. In systems of this type, itis customary to employ a scale associated with the conveyor which isadapted to adjust the feeder so as to control the flow of material atthe discharge end of the conveyor. As is well understood by thoseexperienced with automatic controls, the time lag for material to passfrom the feeder to the scale is critical in the operation of the controlapplied to the feeder. If the rate of correction applied to the feederfor a given weight error is too great relative to the transportationtime lag, a condition of continuous oscillation or 'hunting of thefeeder will occur. The transportation time lag for material to pass fromthe feeder to the scale varies with the conveyor speed and thus theproper rate of correction of the feeder should also vary with beltspeed.For example, a fast belt speed provides'a relatively short time lag andthus the control for the feeder can be set relatively fast-actingwithout hunting. However, if the control response is set as fast aspossible when the belt speed is high and later the belt speed isreduced, the control system will then oscillate because of the increasedtime delay for the material to pass from the feeder to the scale.Conversely, if the control settings are made at the time when the beltspeed is slow, the control will be relatively slow-acting and thus thecontrol action at higher belt speeds will be relatively poor as comparedwith faster control settings.

The present invention eliminates this problem by automatically providinga corrective rate in proportion to speed.

In accordance with one form of the invention, there is provided in asystem for continuously feeding material from a feeder to a continuouslytraveling conveyor, the improvement of means for controlling the weightof material on the conveyor uniformly in accordance with a predeterminedweight. Such improvement includes a first measuring means responsive tothe weight of the material on the conveyor and a second measuringmeans'responsive tothe speed of the conveyor. The improvement furtherprovides control means operative to adjust the feeder output in acorrective direction to obtain the predetermined weight of material andcompensating means effective on the control means and responsive to bothof the measuring means to vary the rate of feeder correction inproportion to conveyor speed, so that the rate of feeder correction isinversely proportional to the time lag between the feeder and the firstmeasuring means.

In one form of the invention, the compensating means comprises anelectrical network in circuit with the control means. The networkincludes a pair of resistances across each of which there is applied avoltage directly proportional to the conveyor speed and the circuitconnections a station 15 at the discharge end of the conveyor.

3,139,217 Patented June 30, 1964 the latter is subject to any differencein voltages across predetermined portions of the pair of resistance-s.

It is another object of the invention to provide control of the flow ofmaterial in ratio to a primary variable by compensation of speed andweight signals.

It is a further object of the invention to provide anticipating actionby employing conveyor speed signals to obtain immediate feedercorrections without waiting for weight errors to appear.

For further objects and advantages of the invention and a more detailedunderstanding thereof, reference may be had to the following descriptiontaken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram of a control system embodying the presentinvention;

FIG. 2 is a schematic diagram of a control system embodying amodification of the invention illustrated in FIG. 1;.

FIG. 3 schematically illustrates the present invention as applied to aratio control system;

FIG. 4 is a schematic diagram of a control system em bodying theinvention and including anticipating action;

to deliver material 12 from a hopper 13 to an endless conveyor 14 whichcarries the material 12 to a discharge The feeder 11 may be of anysuitable type, such, for example, as of the vibrator type, well-known inthe art, where the amplitude of vibration of a trough for the materialis varied by varying the resistance in the electrical circuit to varythe rate of feed of the material. The feeder 11 may also be of theendless belt type with the belt being motor driven and including controlfor varying the speed of rotation, to change the rate of feed 'ofmaterial The the material on the conveyor as its passes thereover. The

other idlers 19 as well as the pulleys 17 are rotatably supported on theconveyor frame (not shown).

The weighing scale Zilmay be of any suitable type such as the typeillustrated in United States Patent No. 1,298,302Davis. Preferably, theweighing scale 20 is of the type which rotates a shaft 21 at a speedproportional to the actual measured flow rate at the scale location,this shaft being connected to a counter 22 so that the numbers on thecounter indicate the integrated or totalized quantity of material passedover the scale. The shaft 21 is connected to a tachometer generator 24or equivalent device for producing a voltage signal proportional to theflow rate of material at the scale. It will be seen that this voltagesignal will take into account both the weight and speed variables.

The feeder 11 is adapted to be automatically controlled from acontroller 26. The controller 26 may be of any of several conventionaltypes but preferably is of the integrating or automatic reset type, suchthat the rate of correction of the feeder 11 is proportional to theerror in weight. With controllers of this type, large errors cause thecontroller to produce faster corrections and the error is reduced to anegligible value under final steady-state conditons. The controller 26is adapted to send the corrective signal to the feeder 11 by way ofsasaai'r the signal path 27. The signal path or link 27 may be eitherelectrical or mechanical in character such as an 7 electrical cable, orequivalent, for transmitting an electrical signal to the feeder 11, orit may be a mechanical connection for transmitting a mechanicalcorrective signal to the feeder 11. Controllers of this type arewell-known in the art and one example is disclosed in United StatesPatent No. 2,666,170-Davis.

The controller 26 is adapted to be associated with compensating meansfor varying the rate of feeder correction in proportion to conveyorspeed so that the rate proportion to the speed of the conveyor 14 andthus the tachometer generator 31 produces an output voltage proportionalto the speed of the conveyor. This voltage is appliedby way ofconductors 34 and 35 to the impedance 29. The conductor 34 has apositive polarity with respect to conductor 35. The impedance 29 andmovable tap 30 may consist of a conventional slidewire or rheostat andbe calibrated, for adjustment from zero to a maximum, the units ofadjustment on scale 28 being calibrated in the desired weight per unitlength of conveyor, for example, pounds per foot. The tachometergenerator 24 which is driven from the same mechanism that operates thecounter 22 of weighing scale 20 delivers a voltage proportional to theactual flow rate passing over the weighing scale 20. This voltage isapplied by conductors 36 and 37, the former having a positive poreversesas the polarity between conductors 42 and 43 reverses. Thus, whenconductor 42 is positive with respect to conductor 43, the correctivesignals are such as to increase the output of feeder 11 and when thepolarity of conductors 42 and 43 reverses, the correction is such astodecrease the feeder output. Conductors 35 and 37 are connected by aconductor 44 to provide a common connectionfor proper comparison of therespective signals. 1

v As mentioned above, the position of the adjustable tap 30 on impedance29 represents the desired or predeter-' mined magnitude of weight perfoot on the conveyor belt 14. To obtain zero pounds per foot on belt 14,the tap 30 is connected to the end of impedance 29 which connects toconductor 35 and to obtain maximum pounds per foot on the belt 14, thetap 30 is connected tothe end of impedance. 29 which connects toconductor 34. With this arrangement, the tap 30 preferably ismechanically connected to a dial adjustment, or equivalent, which islinearly calibrated in the desired weight per foot.

The controller 26 preferably is a relatively high impedance device, suchthat relatively little current is drawn from conductors 42 and 43. Thusthe voltage V between 7 where k is a proportionality factor.

This relationship may be written The voltage V between the junction ofresistors 39 and 40 and conductor 44 represents the measured flow rate FThe measured flow rate F is a product of two variables; namely, themeasured weight per foot W at the This rescale 20 and the measuredconveyor speed S lationship may be written in equation form as thefollowing Equation 2:

and V i.e.the difference between'the potentials of conductors 42 and 43,represents the difference between the desired or predetermined weight Wand the measured Weight W that difference multiplied by the speed S ofbelt 14. This will be seen by subtracting Equation 2 from Equation 1:

and by substitution Equation 3 it will beseen that Thus the potentialdifference between conductors 42 and 43 is zero and this potentialdifference will be Zero regardless of the belt speed S However, whenthere is a weight error, i.e., W W is not zero, there will be adifference in potential between conductors 42 and 43 and that differencein potential, i.e. V V will vary in exact proportion to the speed Sm ofbelt 14. Since the rateof corrective action of the controller 26 isproportional to the potential difference it receives at conductors 42and 43, the rate of correction of the controller 26 will also vary inexact proportion to the speed S of belt 14. This is the proper actionrequired to give the desired effect of optimum control at all beltspeeds S without hunting. For example, if the belt speed S is doubled,the time lag, i.e., transportation time of the belt between the feeder11 and the scale 20 will be'reduced to one-half its former value and thecontrol 26 will correspondingly take corrective action twice as fast fora given weight error. Accordingly, when the control settings are madefor any belt speed S they will be correct regardless of any changes thatmay be made in the belt speed S From the foregoing description of theinvention it will be apparent that various modifications may be made inthe compensating network without affecting the basic concept ofmultiplying the weight error W -W times the belt speed S For example,the tachometer generators 24 and 31 may be of the. alternating currenttype rather than direct current type in which case the potential betweenconductors 42 and 43 will be subject-to a phase reversal instead of apolarity reversal when the Weight error varies from high to low or,vice-versa. In applications where it is not'necessary to vary thedesired weight the measured flow rate signal F may be established bymultiplication of separate Weight and speed measurements such as by anelectrical resistance determined by a weight variable and an electricalvoltage determined by a tachometer generator driven at belt speed on theconveyor belt. FIG. 2 where parts corresponding to those in FIG. 1 havebeen identified With corresponding reference characters. In FIG. 2, itwill be seen that the tachometer generator 24 has been eliminated fromsystem 10A and,

tachometer generator 31 provides both belt speed signals with respect toimpedance 29 and resistors 39 and 40. It

Accordingly, the difference between these potentials, V

v When the measured weight W equals the desired weight Such anarrangement has been illustrated in will be seen that the upper end ofresistor 39 has been connected by a conductor 46 to conductor 34 andconductor 43 has been provided with a movable contact 43a which isadjustable relative to resistors 39 and 40 to Vary the relationtherebetween. The movement of contact 43a is provided by a mechanicalconnection 47 which extends to the scale 20 and is connected to thedeflecting member thereof. Thus the contact 43a is adapted to be raisedor lowered with respect to resistors 39 and 50 depending upon the Weightof the material 12 on the scale 20 While the systems and 10A illustratedin FIGS. 1 and 2 may be used by themselves in applications requiringcontrol of a constant weight per unit length of belt in spite ofvariations in belt speed, such systems have a further advantage in theirease of modification to provide ratio control of the material deliveredat the end of the end of the'conveyor so that there will result thecontrol of a desired blend of the two materials. Such a system has beenillustrated in combined FIG. 3. In FIG. 3 there has been illustrated aprimary variable signal 50 which is applied in the form of a voltagebetween conductors 51 and 52, FIG. 3. The primary variable signal 50represents the rate of flow P of another stream of material 12' whichthe controlled flow of material 12 joins at the discharge end .15 of theconveyor so as to control the desired blend of material 12 with thesecond material 12. As will be seen in FIG. 3, the second material 12 issupplied from a feeder 11 to an endless conveyor 14' to discharge end 15of which is disposed adjacent the discharge end 15 of conveyor 14. Theconveyor 14 is adapted to be driven from a motor M. The material 12 onconveyor 14' passes over a weighing scale which is mechanicallyconnected by linkage 21 to a tachometer generator 24' which in turnproduces the primary variable signal 50. The scale 20 is provided with acounter 22 which is adapted to indicate the integrated or totalizedquantity of material 12 passing over the scale 26. The variouscomponents of the second conveyor may be similar to the correspondingcomponents associatedwithcon- I veyor 14 and thus they have beenidentified with like reference characters except for the addition of aprime. Since the counter 22 provides an indication of the totalizedquantity of material passed over scale 20 on conveyor 14, and sincecounter 22' indicates thetotalized quantity of material passing overscale 2% on conveyor 14?, the combined totals appearing on indicators 22and 22',will provide an indication of the combined flow of materials 12and 12 at the discharge ends 15 and 15' of the conveyors.

The primary variable signal 50, as seen in FIG. 3, is applied to, animpedance 54 having a variable tap or slider 55. The position of tap 55on impedance 54 represents the desired ratio setting for the controlsystem 1913. The ratio is zero when the tap 55 is at the lower end ofimpedance 54 which connects to conductor 52 and the ratio is maximumwhen the tap 55 isat the upper end of impedance 54 which connects toconductor 51. The position of tap 55 may be set relative to a scale 5swhich preferably is calibrated in units of ratio or percentage. Aconductor 57 connects with conductor 52 and a conductor 58 connects tothe adjustable tap 55 so that the potential V between conductors 57 and58 is proportional to the desired flow rate R of the controlled material12, that is the primary variable flow rate P times the percentage Y seton the ratio scale 56. This relationship may be eX- pressed in equationform as:

, measured speed signal S Expressed in equation form:

This subtracted difference signal V is applied to a second controller 60which is adapted to send corrective signals by way of connection 61 tothe variable speed conveyor drive motor 18. The controller 60 is of thesame type as controller 26 and operates in the same manner as previouslydescribed for controller 26. Controller 60 makes no correction if thepotential V; between conductors 53 and 59 is zero but increases conveyorspeed in proportion to a potential V; such that conductor 59 is positivewith respect to conductor 5-1 and decreases the belt speed for thereverse polarity. Since both controllers 26 and 60 are relatively highimpedance devices, they do not draw appreciable current and henceneither upsets nor alters the potential appearing at the input of theother.

The operation of the network illustrated in FIG. 3 is such that a changein primary variable signal 50 causes immediate response in the flow ofmaterial 12 oif thedischarge end 15 of the conveyor 14' in spite of thelong time delay from the feeder 11 to the discharge end 15. If theprimary variable signal 50 changes, or if the ratio adjustment Y ischanged, i.e., changing the position of tap 55 with respect toresistance 54, the speed controller 60 will immediately receive an errorsignal and will immediately correct the speed of conveyor 15 in exactproportion to the initial change. Since there are only small time lags'in the variable speed drive 18, the controller 60 may be set to respondrapidly. The change in speed will not affect the weight controller 26 ifit is in balance, since the potential V between conductors 42 and 44 andthe poten-- tial V between conductors 43 and 44 will both change inexactly the same proportion to speed S of conveyor 14. However, thespeed change Will alter the weight per linear foot on the conveyor 14 atthe feeder end of conveyor 14 and this change in weight will laterappear at the weighing scale 20 causing an error in the weightcontroller 26. The controller 26 will then eliminate this error bysending corrective signals to the feeder 11. Similarly,

changes in the operating characteristics of the feeder 11' do not causean error voltage to'appear at the speed controller 60 but only requirecorrection by the Weight controller 26. Accordingly, the two controllers26 and 60 operate entirely independently of each other. The speedcontroller 60 assumes that the 'Weight per foot on the conveyor 14 isalways correct, and based on this assumption, it controls the deliveryof material 12 at the discharge end 15 of conveyor 14 at the desired orpredetermined value. The weight controller 26 corrects the output-offeeder 11 to deliver the same weight per foot on the belt 14 that isassumed in the calibration of the speed controller 60. The

weight controller 26 always resets to the same point regardless of thespeed of belt 14 but its dynamic response is proportional to belt speedas previously described. The

combination of these desired actions is obtained by using the measuredspeed and desired weight signals S and W in the manner described, oneset of signals sufficing for combined correct operation of bothcontrollers 26 and 60.

Another difiiculty encountered with conventional systems is that a timedelay occurs between the change in belt speed and corrective action ofthe feeder due to the transportation delay between the feeder and thescale. If the conveyor speed increases, for example, the weight per footof the belt at the feeder will decrease and this change will area,

travel along theconveyo-r until it reaches the scale before corrective.action is initiated by the scale. Accordingly, a weight error will occurfor this time period and for the additional time period required for thescale to complete its corrective action. In accordance with the presentinvention, there is provided means for anticipating this action and forhaving the weight controller correct the feeder immediately following achange in belt speed without waiting for the weight error to appear atthe scale. Such an arrangement is illustrated in the system of FIG. 4.From the following description of FIG. 4, it will be seen that anadjustable portion of the belt speed signal is applied in series withthe weight controller output to produce an immediate correction of thefeeder following a change in 'belt speed. InFIG. 4, it will be seen thatthe system 16C utilizes the same basic components as the system in FIG.1 and these have been identified by corresponding reference characters.a

, 'As may be seen in FIG. 4, the voltage V appearing between-conductors42 and 44- which is similar to the voltage appearing between thoseconductors in FIG. 1, also appears between conductors 65 and 66, FIG. 4,which connect an impedance 67 in parallel with the portion of impedance29 connected between conductors 42 and 44. The impedance 67 has avariable tap or slider 68 to provide an adjustment of the magnitude ofthe anticipatingv action. The magnitude of impedance 67 is very. high inrelation to the magnitude of impedance 29 so that negligible current isdrawn from the tap 30. The variable tap 68 is connected to one of theoutput terminals of a controller 26a by a conductor 70 and the otheroutput terminal of controller 26a is connected by a conductor 71 to thefeeder 11; The controller 26a in FIG. 4 is similar to controller 26inFIG. 1 except'that the controller corrective output signals, shown as asimple line 2'7 in FIG. 1,

are shown in FIG. 4 as a voltage appearing between the two outputconductors 70 and 71, conductor 71 increasing positively with respect toconductor 70 to give an increase I in the rate of flow from the feeder11. The resultant voltage V from the anticipating adjustment of tap 68on impedance 67 is applied, by conductor 70 from controller 26aand-conductor 72, which connects to conductor 66 and the correspondingend of impedance 67, to the feeder 11 so that an increase in belt speedwill call for an increase of feeder output. A change in belt speedcauses an immediate proportional change in the signal to the feeder 11plete the required change in the feeder output over and a above thatmade by the anticipating action since it contains an integrating orautomaticreset function which continues to make corrections until theweight error is zero. Thus it will be seen that the final 'or-steady-state value of feeder output is established by controller 26a and theanticipating action applied between conductors and 72 onlysupplies aninitial estimated corrective action. The controller 26a insures 'final'accuracy but the anticipatingaction provides the desired immediateresponse.

It is to be noted that the speed signal alone appearing betweenconductors 34 and 35 might be applied to impedance 67 directly and stillproduce the same action as far as has been heretofore described.However, if applied in that manner, the amount of anticipating signalwill not be correct at dilferent belt speeds. The reason for this isthat'it is the percentage of speed change that is critical and not theabsolute value of speed change. I

Accordingly, if the Weight setting is doubled for a given speed atone-half speed will produce only one-half as.

much change in voltage from the tachometer generator 31. This loss isovercome in the system of FIG. 4 by using the signal available at tap 30which has double the position under the stated conditions. As a result,there'is obtained the same amount of anticipating action for eachpercentage change in. speed regardless of Whether the flow rate isachieved'by a higlrweight at a low speed or vice-versa.

It will be obvious that automatic controller 26a need not be of the typethat delivers a volt'agesignal to the feeder 11 as illustrated in.FIG.4. For example, the controller 26a could position a rheostat or amechanical speed-setting lever or the like associated with the feederdevice.

FIG. 5 shows in greater detail one means of asserting control throughthe controller when the speed and hence rate of feed of the materialfeeder ll of the automatic control system of FIG. 1, is to be varied.Since thesystern is in most respects similar to FIG. 1, similar numbershave been used to designate similar parts and it will be understood thattheir function is the same. Involved here is a specific system betweenthe controller 26 and the feeder ll. Specifically, the controlleroperates in this instance by means of a reversible motor which,

through an appropriate shaft and mechanical connection 81, drives acurrent varying rheostat 82a82b in series with variable speed motor 83across an appropriate power a It is the variable speed motor 83 whichdrives the feeder through shaft 84 and other ap- More specifically, thecontrollerserves to provide an error signal either through line 27asupply Ll and L2.

propriate connection.

to Winding 80a of the reversible motor drive if the motor is to beoperated in one direction or through line 27b and winding 80b if themotor is to be run in the'other direction in order to correct theposition of movable tap 32a with respect to slide wire or otherresistance element 82b. The controller thus acts as a switching elementto connect the appropriate field winding 80a or 80b across power linesL1 and L2 Which also serve to supply energization to the drive motor 83.It will be apprecaited that this showing is highly schematic but itispresented to show in principle one type of system of the type generallytaught by Davis Patent 2,666,170.

It will be also obvious that different devices could be used to handlethe anticipating signal with such control-- lers, such as additionalamplifiers, or rheostats, or the like.

ed all such conveyors are driven at substantially propor- W tionalspeeds. I

It is to be understood that the invention is not limited to the specificarrangements shown and that further modi- I fications may be made withinthe scope of the appended claims.

I claim: v v g 1. A system for controlling the desired blend of twomaterials comprising first conveyor means having a variable speed driveand receiving material from a feeder, second conveyor means beingadaptedto transport mate-j rial to a location adjacent thedischarge endof said first conveyormeans to provide a blend of material from both ofsaid conveyor means, first measuring means producing a first signalproportional to the mass flow rate of material on said first'conveyormeans, second measuring means producing a second signal proportional tothe speed of said first conveyor means, third measuring means producinga third signal proportional-to the rate of flow of material from saidsecond conveyor means, first control means operative to correct saidfeeder output until said first and second signals are equal, and secondcontrol The invention is also applicable to a plurality of; feeders, andto a plurality of conveyors in series provid- 9 means operative toadjust said variable speed drive of said first conveyor means until saidsecond and third signals are equal whereby the mass flow rate ofmaterial on said first conveyor means is adjusted in proportion to theflow rate of material on said second conveyor means.

2. In a system for controlling the mass fioW rate of material on aconveyor in proportion toa primary variable, the conveyor having avariable'speed drive and receiving material from a feeder, thecombination of first measuring means producing a first signalproportional to mass flow rate, a second measuring means producing asecond signal proportional to conveyor speed, third measuring meansproducing a third signal proportional to said primary variable, firstcontrol means operative to correct the feeder output until said firstand, second signals are equal, and second control means operative toadjust the variable speed drive of saidconveyor until said second andthird signals are equal.

3. The combination according to claim 2 including adjusting means incircuit with all of said measuring means and both of said control'means,said adjusting means being operative to vary the amount of said thirdsignal applied to said second control means for governing the ratio ofmass flow rate to said primary variable. y

4. The combination according to claim 2 including adjusting meansoperative to vary the amount of said second signal applied to both ofsaid control means for governing the weight per linear foot of materialon the conveyor. I

5. The combination according to claim 2 including first adjusting meansin circuit with all of said measuring means and both of said controlmeans, said first adjusting means being operative to vary the amount ofsaid third signal applied to said second control means for governing theratio of mass fiow rate to said primary variable, and second adjustingmeans in circuit with both of said control means and operative to varythe amount of said second signal applied to both of said controlrmeansfor govern ing the weight per linear foot of material on the conveyor.

References Cited in the file of this patent UNITED STATES PATENTSJohansen Dec. 30, 1952 2,626,787 Harper Jan. 27, 1953 2,969,227 24, 1961Ludwig Jan.

1. A SYSTEM FOR CONTROLLING THE DESIRED BLEND OF TWO MATERIALSCOMPRISING FIRST CONVEYOR MEANS HAVING A VARIABLE SPEED DRIVE ANDRECEIVING MATERIAL FROM A FEEDER, SECOND CONVEYOR MEANS BEING ADAPTED TOTRANSPORT MATERIAL TO A LOCATION ADJACENT THE DISCHARGE END OF SAIDFIRST CONVEYOR MEANS TO PROVIDE A BLEND OF MATERIAL FROM BOTH OF SAIDCONVEYOR MEANS, FIRST MEASURING MEANS PRODUCING A FIRST SIGNALPROPORTIONAL TO THE MASS FLOW RATE OF MATERIAL ON SAID FIRST CONVEYORMEANS, SECOND MEASURING MEANS PRODUCING A SECOND SIGNAL PROPORTIONAL TOTHE SPEED OF SAID FIRST CONVEYOR MEANS, THIRD MEASURING MEANS PRODUCINGA THIRD SIGNAL PROPORTIONAL TO THE RATE OF FLOW OF MATERIAL FROM SAIDSECOND CONVEYOR MEANS, FIRST CONTROL MEANS OPERATIVE TO CORRECT SIDEFEEDER OUTPUT UNTIL SAID FIRST AND SECOND SIGNALS ARE EQUAL, AND SECONDCONTROL MEANS OPERATIVE TO ADJUST SAID VARIABLE SPEED DRIVE OF SAIDFIRST CONVEYOR MEANS UNTIL SAID SECOND AND THIRD SIGNALS ARE EQUALWHEREBY THE MASS FLOW RATE OF MATERIAL ON SAID FIRST CONVEYOR MEANS ISADJUSTED IN PROPORTION TO THE FLOW RATE OF MATERIAL ON SAID SECONDCONVEYOR MEANS.